U-extraction-improvements in elimination of mo by use of ferric ion



United States Patent U-EXTRAC'IIONMPRQVEMENTS IN ELIMINA- TION OF Mo BY USE OF FERRIC ION 8 Claims. (Cl. 23-145) 7 This invention relates to the purification of uranium and more particularly to the separation of uranium from molybdenum.

An eflicient process for the purification of uranium is the solvent extraction process whereby uranium values may be extracted by a water immiscible organic solvent" from an aqueous solution of uranyl nitrate. By this process the uranium may be separated substantially cornpletely from most other substances since the uranium has a greater solubility in the organic solvent than the contaminating materials. However, it has been found that molybdenum in the presence of phosphate ions, which are often present in the solution, especially when the solution is one obtainedby acid digestion of a uranium containing ore, appears to form a complex with the phosphate which extracts along with the uranium values.

It is an object of the present invention to provide a process for the separation of uranium from molybdenum.

It is a further object to provide an organic solvent extraction process for the separation of uranium from molybdenum. Other objects will become apparent from the following description ofthe invention.

By the process of the present invention uranium values may be separated from molybdenum values by extracting the uranium values with a Water immiscible organic solvent from an aqueous solution of uranyl nitrate and molybdenum values to which has been added ferric ions.

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- 52 P ability to dissolve uranium values. A few examples of such solvents are methyl isobutyl .ketone, dibutylicarbitol;

dibutyLcellosolve and 'diethyl ether; the latter beingja particularly suitable solvent for the process ofthelpresv ent invention.

The extraction may be carried out by contacting fthe 7 aqueous phase with the'solvent in a batch process a continuous counter current extraction process. In either case it has'been foundethatefiicient extraction. of

the uranium may be obtained by'oontactingthe aqueous phase with a volume of organic solvent totalingapp'roximately six times the volume of aqueous solution.

Variations of the HNO concentration of the aqueousfeed solution and the extracting ether were found to have a complexfetfect upon the extraction ratio of Mo/U. In addition to the effect of the acid concentration upon the Mo/U extraction ratio is the effect of theacid con centration in the organic solvent upon the mechanical operation of the extraction process." Extraction with ether containing no HNO results in the formation of a solid in the ether phase, presumably a hydroxy complex of uranium, during the extraction process which interferes mechanically with the extraction. The presence of HNO in the ether prevents 'the formation of this solid. For the processof the present invention, it is desirable to contact theaqueous phase with an ether having approximately a 1 N: HNO concentration. This concentration The concentration of uranium in the solution may vary within wide limits. For example, the extraction may be carried out by contacting the uranyl nitrate in the solid phase, in which phase it exists with six molecules of water of hydration per molecule, viz., UO (NO 6H O,

, centration of the UO2(NO as low as practical consistent with the other factors which must be considered for an eflicient process. A suitable solution usable in the process of the present invention is a solution contain-' ing approximately 350 grams of UO (NO per liter of solution.

The addition of salting out agents to the aqueous'phase prior to contacting with the organic solvent increases the distribution coefiicient, that is, the ratio of uranium in the organic solvent phase to that remaining in the aqueous phase after contacting the aqueous phase with the water immiscible organic solvent. Suitable salting out agents include sodium nitrate, calcium nitrate, copper nitrate and aluminum nitrate.

Suitable organic solvents include any of the known Water immiscible organic solvents showing a selective of HNO prevents the formation of this solid and inad dition results in a favorable Mo/ U extraction ratio. The most favorable results in, the present process are obtained when the HNO concentration of the feed solution is beloW approximately 0.2 N. Satisfactory results were ob tained, however, with feed solutions having 2. HNO;.; concentration above 1 N. e e l The-following examples illustrate but do not limit the invention; 1 V

' EXAMPLE I The solution containing uranium and molybdenum used in the presentexample was obtained by digestion of pitchblende ore. 95.5 pounds of an ore slurry containing 69.0% by weight (30 kg.) of dry ore assaying 6i1".9% in U 0 on a dry basis was digested with 2418 liters of =36 HNO This Lamounts to 1.8- stoichiornetn'c amounts of HNO based upon the assumption that 7 moles ofHNO per mole of U O 'are necessary for reaction. 7 7 1' V The ore slurry was brought to a temperature of about C. and the acid. added over. a period of approximately'20 minutes. 2.4 liters of 66 B. sulfuric acid were then added to the digestion mixture'to precipitate the lead and radium values extracted from the ore by the digestion. This precipitate and undissolved material were removed by filtering and the filtrate" containing the uranium and molybdenum valu es was t'reated with 7 kg.. of BaCO .toremove any excess-so iofiv until the boiling point of the solution reached C.

The above concentration step or boil down{ serves to dehydrate some of the silica extracted from thefore Molybdenum forms a complex-with silica, silicomolybdic 'acid whichlike the phosphate complex is soluble in ether. Thus this: boil down step decreases the amount of silica available to complex the molybdenum and hence tends to decrease the amount of molybdenum subsequently extracted by the ether. e

' The solution remaining after the boildown step -was 70 diluted to a volume of 3.7 gal. havingan approximate? UO (NO concentration-of 0.42 gm./ml. 36,0';gm.'of 'Fe(NO -9H O were then added and the solution" wee except that;no"Fe(NO' -9H O 'was'added the ratio of MoO /UO(NO in the extract phase increased to 41 parts per million. r

The "extraction" in these tests was carried out in a packed column. The column was first filled with diethyl ether and the feed rates adjusted to a flow rate" of l vloume of aqueous feed per 2 units of volume of diethyl ether. The runs were prolonged until three times the ether volume of the packed sections had been displaced by the incoming solvent.

EXAMPLE II The solutions used in the present example were also obtained by HNO digestion of pitchblende ore. 95.5 lbs. of an ore slurry identical in composition to that of Example I were digested with 18.0 liters of 36 B. HNO This amounts to 1.3 stoichiometric amounts of HNO based upon the assumption that 7 mols of HNO per mole of U 03 are necessary for reaction; The ore slurry was first brought to 70 C. and the acid added over a period of 20 minutes. Digestion was continued until N0 ceased coming ofi at which time the slurry temperature was approximately 100 C.

4.0 k g. of Ba(NO dissolved in gal. of H 0 were then added to the hot digestion solution. This amount of Ba(NO is based on a ratio of 400,000 parts of Ba to 1 part of the radium contained in the ore digested. This ratio is the assumed optimum for radium removal by a sulfate precipitation. To cause this sulfate precipitation 1.28 liters of 66 B. H280 diluted with 1.3 liters'of H O were immediately added after the Ba(NO addition. The amount of H 80 added is stoichiometrically equivalent to the Ba(NO added and to the Pb content of the ore assayed at 6% PbO. The digestion was continued for 30 minutes. The solution was then cooled to 4060 C. and filtered and washed. a

The filtrate and washings were combined and dilutedjt 17.2 gal. to give a UO (NO concentration of approximately'OA gm./ml. of solution. This solution was then heated to boiling and 2.15 kg. of BaCO added to assure complete removal of sulfate ions. After digestion for one hour the solution was filtered to remove the BaSO; and the filtrate again diluted to 17.2 gal.

The solution was then boiled down to 120 C., diluted, and the pH adjusted to 0.7 by the addition of Na CO The final solution volume was 9.3 gal. with a computed UO (NO content of 0.74 gm./ml.

3.0 gal. of this solution were then diluted to 3.6 gal. and 342 gm. of Fe(NO -9H O added. The solution EXAMPLE III and 2700- parts of MoO per million parts of UO (NO was then saturated with NaNO and filtered. The final solution contained 0.396 gm./ml. of UO (NO 0;025 gm./ml. of Fe(NO -9H O and 2l00'parts of M00 per million parts of UO (NO The HNO concentration was 0.043 N. This solution was extracted with diethyl ether 1 N in HNO in the same manner as the previous example. The M00 content of theextract was 15 parts M00 per million parts of UO (NO Another portion of the 9.3 gal. of solution containing 0.74 gm./ml. of UO (NO was treated similarly with the exception that no Fe(NO -9 H O was added prior to the extraction step. In this instance the ether extract contained 188 parts of M00 per million parts of 2( a):-

ml. portions of this solution were treated with varying amounts of ferric nitrate and saturated with NaNO 30 ml. portions of the saturated solutions were shaken with three ml. portions of diethyl ether 1 N in HNO The results of these 'experiments'are shown in the following table.

Table I FG(NO3)3-9H O, UOKN 03):, M1003 ILDJD. Solution No. grn. m1. gm./ml. UO2(NO3)2 in extract 0. 005 0. 35 186 O. 016 0. 34 39 0. 039 0. 33 25 0. 078 0. 33 16 0. 164 o. 32 n The great reduction in the ratio of the Mo/U extracted in the presence of even a very small concentration of Fe+ ion is demonstrated by the results from solution one where the presence of Fe+ reduced the MoO /UO (NO ratio by a factor of better than 2.2, andis demonstrated further in the subsequent tests where slight increases in Fe+ ion concentration reduced the ratio by even greater factors.

As the above examples illustrate, the addition of 'ferric' ion to. the aqueous phase decreases the extraction of molybdenum by the ether. The extraction of the molybdeuum is assumed to be due to the formation of phosphomolybdic acid which is ether soluble'whereas molybdeuum values per se are not. The addition of the ferric ion is thought to cause the formation of a strong complex of ferric ion and phosphate ion thus preventing the formation of the ether-soluble phosphomolybdic complex.

Aside from the advantage of the process of the present invention in obtaining a product of higher-purity is the elimination of operating difliculties caused by molybdenum in the extraction operation. The molybdenum in the high concentrations present without the use of ferric ion in the extraction process forms solids of some complex type which accumulate at the interfaces in the counter-current extractor. If the molybdenum is extracted into the ether it also forms solids during-the stripping operation wherein the ether containing the uranyl nitrate is contacted with water to remove the uranium values therefrom. These solids result in mechanical interference in the extractionoperations.

- From the foregoing description, it will be apparent to those skilled in the art that the instant invention provides a practical, inexpensive and relatively simple method ofjobtaining uranium substantially free from molybdenum.. V a

It is to be understood that all matter hereinbefo're set forth is to be considered as illustrative and not in a limiting sense, and that the scope of the invention concept is limited only by the appended claims.

Weclaim: i

'1. A method of recovering uranitun values from aqueous solutions containing uranium values and molyb denum values which comprises adding ferric ions to the solution, and thereafter extracting the uranium values by contacting the solution with a substantially water immiscible selective organic solvent.

2. A process for obtaining uranium values substantially free from molybdenum from aqueous solutions containing uranium values, molybdenum values, and phosphate ions which comprises incorporating ferric ions in the solution to complex the phosphate ions thus preventing the formation of organic solvent soluble phosphornolybdates, and thereafter contacting the solution with a substantially water immiscible organic solvent to extract the uranium values from the solution.

3. The process of claim 2 wherein the organic solvent is diethyl ether approximately 1 N in respect to I-INO 4. The process of claim 2 wherein NaNO is added to the solution prior to contacting said solution with the organic solvent.

5. The process of claim 2 wherein NaNO is added to the solution prior to contacting said solution with the organic solvent and said organic solvent is diethyl ether approximately 1 N in respect to HNO 6. A process of obtaining uranium substantially free from molybdenum from an aqueous solution of uranyl nitrate containing in addition molybdenum values, phosphate ions and dissolved silica which comprises heating the solution to dehydrate a portion of the silica thereby removing it from the solution, and thereafter adding ferric nitrate to the solution and contacting said solution with diethyl ether to extract the uranyl nitrate therefrom.

7. A process of obtaining substantially pure uranyl nitrate from a pitchblende ore which in addition to U 0 contains lead, radium, molybdenum, silicon and phosphorus values which comprises digesting said ore in aqueous solution of HNO separating the dissolved lead and radium values from the solution obtained by the 8. A process of obtaining uranyl nitrate substantiallyv free from molybdenum from an aqueous solution of uranyl nitrate which also contains dissolved molybdenum values and phosphate ions which comprises adding ferric nitrate to said aqueous solutionof uranyl nitrate in order to complex said phosphate ions and then extracting uranyl nitrate from said aqueous solution with diethyl ether.

References Cited in the file of this patent UNITED STATES PATENTS Hixson et al. Ian. 7, 1941 OTHER REFERENCES Misciatelli: Chemical Abstracts, vol. 23, page 1554 (1929). 

1. A METHOD OF RECOVERING URANIUM VALUES FROM AQUEOUS SOLUTIONS CONTAINING URANIUM VALUES AND MOLYBDENUM VALUES WHICH COMPRISES ADDING FERRIC IONS TO THE SOLUTION, AND THEREAFTER EXTRACTING THE URANIUM VALUES BY CONTACTING THE SOLUTION WITH A SUBSTANTIALLY WATER IMMISCIBLE SELECTIVE ORGANIC SOLVENT. 